phone built at NEL especially for TRIESTE. 

 In certain areas reception is poor even 

 though the range is well within that adver- 

 tised — e.g., when the vehicle might be in a 

 deep canyon, and echoes produce weak or 

 garbled messages. Similar communicating 

 problems may be encountered in shallow 

 slant-range modes between surface vessels 

 and submerged vehicles. Thermal discontin- 

 uities occur where the transmission is en- 

 tirely masked or where the same signal ar- 

 rives at closely-spaced, but different time 

 intervals (as a result of multipath transmis- 

 sion). Optimum surface-to-subsurface com- 

 munications occur when the surface ship is 

 directly or nearly directly over the submers- 

 ible and acoustical signal paths are normal 

 to near-surface temperature (density) discon- 

 tinuities. Similarly, good communication is 

 usually obtained between two or more sub- 



mersibles at depths below the thermocline. 

 There are no standard practices for fre- 

 quency of communications between submers- 

 ible and support craft. Some operators insist 

 on immediate surfacing if communications 

 are lost, while others allow operations to 

 continue for some specified time and then, if 

 communications are still out, require surfac- 

 ing. Still others merely wait to see what 

 went wrong after the vehicle's operator de- 

 cides to surface (4). 



Tethered submersibles, such as GUPPY 

 and KUROSHIO II, rely on a hard line com- 

 munication system built into the power-sup- 

 plying umbilical between surface ship and 

 submersible. From the information availa- 

 ble, it is unclear whether or not a wireless 

 means of communication is available in the 

 event that the cable parts. Some shallow 

 diving vehicles, e.g., the NAUTILETTE se- 



TABLE 14.7 MANNED SUBMERSIBLE UNDERWATER TELEPHONES 



Manufacturer 



Aquasonics Engineering Corp. 

 San Diego, Calif. 



Hydro Products 

 San Diego, Calif. 



Model No. 



DV-811 



Carrier Frequency 

 (kHz) 



42 



8.0875 



Max Range 

 (yd) 



4,000 

 3,000 



4,000 



Helle Engineering 

 San Diego, Calif. 



STRAZA Industries 

 El Cajon, Calif. 



25.3-28.5 



42 



8-11 



8.0875 

 8.0875 



8.3-10.7 



8.0875 

 8.0875 



4,000 



2,000 

 10,000 



15,000 

 15,000 



7,500 



15,000 

 20,000 



SUBCOM SYSTEMS, LTD 

 No. Vancouver, B.C. 



100S-20A 



110S-20 

 1278-20 



8.075 or 25 



8.0875 

 25 



6,000 

 3,000 

 6,000 

 3,000 



Westinghouse Underseas Div. 

 Annapolis, Md. 



400A 

 41 5A 



8.0875 

 8.087 



25,000 

 10,000 



679 



